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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Background to our Approach We had developed a system to perform sentence filtering  Sentence filtering involves classifying sentences based on whether or not they are relevant to a given scenario.  We reported F-measure results of approximately 55% on a management succession task (Stevenson & Greenwood, 2005). For participation in the LLL challenge we extended this system  We moved to extracting interactions rather than sentence filtering  We extended the pattern representation Previously we had represented sentences using the verbs in the sentence and their direct arguments.

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System We represent extraction patterns as paths in a dependency tree  Dependency trees represent text by linking each sentence word with those words which directly modify it.  For example the noun phrase “the brown dog” is represented by two dependency relations:  In these experiments we used MINIPAR (Lin, 1999) to generate the dependency trees from which the extraction patterns were taken.  The supplied dependency relations were not used due to time constraints of adapting our approach to the task. Extraction Patterns the browndog det adj

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Learning Extraction Patterns Iterative Learning Algorithm 1.Begin with set of seed patterns which are known to be good extraction patterns 2.Compare every other pattern with the ones known to be good 3.Choose the highest scoring of these and add them to the set of good patterns 4.Stop if enough patterns have been learned, else repeat from step 2. Rank Patterns Candidates Seeds

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Pattern Similarity We determine the similarity between two patterns using a vector space model inspired by that commonly used in IR.  Each pattern can be represented by a set of pattern element-filler pairs  The set of pattern element-filler pairs in a corpus forms the basis for a vector space where the value is 1 if a pattern contains the pair, 0 otherwise. The similarity of two patterns can then be computed as: This is the cosine measure augmented with a matrix W which lists the similarity between each pattern element-filler pair.  The similarity between pattern element-filler pairs is computed using a WordNet similarity measure proposed by Banerjee and Pederson (2002) referred to as Adapted Lesk.

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Acquiring Patterns We use this approach to learn patterns containing a known agent or target from the training data. The texts are pre-processed to include AGENT and TARGET as semantic class labels. We restricted certain terms (e.g. repress) to domain specific senses in WordNet for similarity calculations.  We started from the 30 verbs in the PASBio project  28 further other nouns and verbs were also restricted At each iteration of the algorithm we accepted up to 4 new patterns which were within 0.95 of the best pattern being accepted. The algorithm was allowed to run until no more patterns could be acquired.

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Extracting Relations Text from which we wish to extract relations is processed to produce extraction patterns in the same way as before. Any pattern which matches an acquired pattern is used to extract information.  The acquired patterns match with AGENT and TARGET matching anything  Not all patterns contain both an AGENT and TARGET so post- processing links part relations together. So for example  The pattern verb[v/stimulates](subj[n/AGENT]+obj[n/TARGET])  Matches against verb[v/stimulates](subj[n/GerE]+obj[n/cotD])  Resulting in the interaction GerE  cotD

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Challenge Evaluation We submitted three runs for evaluation  Baseline: A simple baseline system which pairs all dictionary elements in a sentence with each other in both orders.  Basic: A system trained on the basic data set without coreference as provided for the LLL-05 challenge.  Expanded: A system trained on the basic data set augmented with 78 automatically acquired weakly labelled MedLine sentences. The basic and expanded systems differ only in the training data used to acquire the extraction patterns.

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Challenge Evaluation SystemPrecisionRecallF-measure Baseline10.6% (53/500)98.1% (53/54)19.1% Basic22.2% (6/27)11.1% (6/54)14.8% Expanded21.6% (8/37)14.8% (8/54)17.5% The baseline system did not achieve 100% recall as some constructs, such as “… A activates or represses B…” requires two interactions between A and B to be recognised. Both approaches have low recall but a precision twice that of the baseline system. While the performance is low it seems that supplying extra training data improves the performance of our approach.

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Analysis If we examine the algorithm at each iteration instead of just the final result we can see that:  The seed patterns are unable to extract a single interaction, i.e. the initial F-measure is zero.  As the seeds do not extract relations the performance of the system is solely due to the acquired patterns.  The algorithm is fairly resilient to the acquisition of bad patterns, i.e. with few exceptions, the F- measure steadily increases.

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Conclusions We used a pattern representation based on dependency trees and an iterative algorithm to learn representative patterns.  The seed patterns were not well suited to the task and future work will include experimenting with different seed sets.  The small amount of training data seems to hinder our approach (adding 78 extra sentences saw a 2.7% increase in F-measure) The similarity measure we adopted seems well suited to this task where similar meaning can be conveyed in different ways.

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August 7th 2005LLL05: Automatically Acquiring a Linguistically Motivated Genic Interaction Extraction System Future Work We intend to try dependency parsers other than MINIPAR to see if they are more suited to biomedical texts. We are already looking at other pattern representations to see if they are more suited to the task/domain. We intend to continue our work on sentence filtering as this would provide a useful first step in any extraction system.